This invention relates to a liquid epoxy resin composition which causes minimal warpage, has improved adhesion to the surface of silicon chips and especially photosensitive polyimide resins and nitride films, and stability against thermal shocks and is thus suitable as a sealant. It also relates to a semiconductor device which is sealed with the liquid epoxy resin composition.
The trend toward smaller sizes, lighter weights and increased capabilities in electrical equipment has led to a shift in the dominant semiconductor mounting process from pin insertion to surface mounting. Progress of semiconductor devices toward a higher degree of integration entails the enlargement of dies having a size as large as 10 mm or more per side. Also an increased number of pins per package has brought on a ball grid array (BGA) in which the substrate has a size as large as 30 mm or more per side. When a semiconductor device using such a large size die or substrate is encapsulated with a sealant, residual stresses left after the cure of the sealant cause the package to warp, which impedes close bonding of balls upon mounting.
For semiconductor devices using such large size dies, greater stresses are applied to the die and the sealant during solder reflow. Such stresses are problematic because separation occurs at the interface between the sealant and the die or substrate, the package cracks upon substrate mounting, and delamination and cracking occur after a thermal cycling test, leading to electrical failure.
An object of the invention is to provide a liquid epoxy resin composition serving as a sealant which is successful in reducing internal stresses after curing and causing only minimal warpage, and which ensures reliability in that it is well adherent to the surface of silicon chips and especially photosensitive polyimide resins and nitride films, does not deteriorate under hot humid conditions as encountered in PCT (120xc2x0 C./2.1 atm), and does not peel or crack over several hundred cycles of thermal cycling between xe2x88x9265xc2x0 C. and 150xc2x0 C. Another object of the invention is to provide a semiconductor device which is sealed with the cured product of the liquid epoxy resin composition.
It has been found that when a liquid epoxy resin composition comprising (A) a liquid epoxy resin, (B) an curing agent, (C) a curing accelerator, (D) an inorganic filler, and (E) a silicone-modified resin in the form of a copolymer of an epoxy or phenolic resin with an organopolysiloxane cures into a product having a specific Tg and a specific dynamic viscoelasticity behavior, the cured product is effectively adherent to the surface of silicon chips and especially photosensitive polyimide resins and nitride films and is fully resistant to heat and thermal shocks. Due to reduced internal stresses in the cured product, the semiconductor device encapsulated therewith experiences minimal warpage. Then the composition is suited as a sealant for large die or substrate size semiconductor devices.
The present invention provides a liquid epoxy resin composition comprising (A) a liquid epoxy resin, (B) a curing agent, (C) a curing accelerator, (D) an inorganic filler, and (E) a silicone-modified resin. The silicone-modified resin (E) is a copolymer of an alkenyl-containing epoxy resin or alkenyl-containing phenolic resin with an organopolysiloxane of the following average compositional formula (1):
xe2x80x83HaRbSiO(4xe2x88x92axe2x88x92b)/2xe2x80x83xe2x80x83(1)
wherein R is a substituted or unsubstituted monovalent hydrocarbon group, xe2x80x9caxe2x80x9d is a number of 0.01 to 0.1, xe2x80x9cbxe2x80x9d is a number of 1.8 to 2.2, and a+b is from 1.81 to 2.3, having 20 to 400 silicon atoms per molecule, the number of hydrogen atoms directly bonded to silicon atoms (SiH groups) being 1 to 5, the copolymer resulting from addition reaction of alkenyl groups on the epoxy or phenolic resin with SiH groups on the organopolysiloxane. When the liquid epoxy resin composition is cured, the cured product should have a glass transition temperature (Tg) of 30 to 120xc2x0 C. and a ratio of a dynamic viscoelasticity at 30xc2x0 C. or lower to a dynamic viscoelasticity at 150xc2x0 C. or higher of at least 100.
The invention also provides a semiconductor device which is sealed with the liquid epoxy resin composition in the cured state.